Interpretive Summary: Compounds primarily attractive to males are known for many tephritid fruit fly species. For the solanaceous fruit fly, Bactrocera latifrons, the best male attractant known to date has been a combination of the chemicals alpha-ionol, sometimes referred to as latilure, and cade oil. The cade oil had previously been found to synergistically enhance the attractiveness of alpha-ionol to male solanaceous fruit flies. Field tests were conducted with seven compounds present within cade oil which had been reported elsewhere to potentially provide some level of synergistic enhancement of the attraction of alpha-ionol to male solanaceous fruit flies. Field trials using sterile sexually mature flies, showed that four of these compounds (eugenol, isoeugenol, dihydroeugenol, and 4-ethyl-2-methoxyphenol) showed relatively greater synergistic attractiveness than the other three compounds. One of these compounds (eugenol) was selected for further field studies with wild flies. Eugenol and alpha-ionol, however, were unable to provide attraction comparable to that of cade oil and alpha-ionol in tests with wild fly populations. Although the research has not yet resulted in an improved male lure, the identification of active components of cade oil provides further insight into the male attractant for B. latifrons and opens additional paths of research which could lead to its improvement. Additionally, the results can potentially contribute to further understanding of tephritid fruit fly male lures, overall, as eugenol is very similar to methyl eugenol, the most powerful of the tephritid fruit fly male lures.

Technical Abstract:
Cade oil, a commercially available essential oil produced by destructive distillation of juniper (Juniperus oxycedrus L.) twigs, is known to synergize the attractantcy of alpha-ionol to male Bactrocera latifrons (Hendel). Through chemical fractionation and outdoor olfactometer-based bioassays, seven compounds in cade oil were identified which potentially could provide some level of synergism. Tests with sterile laboratory flies showed that four of the seven compounds (eugenol, isoeugenol, 2-methoxy-4-ethyl phenol, and 2-methoxy-4-propyl phenol), together with a closely related compound not found in cade oil (2-methoxy-4-methyl phenol), are capable of synergizing the attractiveness of alpha-ionol to male B. latifrons under field conditions. The similarity in structures of these five synergistic compounds shows that there is a response to a core 2-methoxy phenol structure, with fly response little affected by some variation in the composition of the side chain on the number 4 carbon. Because identified synergists were structurally quite similar, only one compound (eugenol) was selected for further field studies. Eugenol and alpha-ionol, however, were unable to provide attraction comparable to that of cade oil and alpha-ionol in tests with wild fly populations. Although the research has not yet resulted in an improved male lure, the identification of active components of cade oil provides further insight into the male attractant for B. latifrons and opens additional paths of research which could lead to its improvement.